Photosynthetic membranes. 54. Mathematical modeling of pilot-plant photomineralization of chlorophenols in aqueous solution, by photocatalytic membranes immobilizing titanium dioxide

Photomineralization of 4-chlorophenol, 2,4-dichlorophenol, and pentachlorophenol, in 9.9 × 10-4-3.8 × 10-5 M aq. solns., in the presence of stoichiometric hydrogen peroxide, was studied using PHOTOPERM CPP/313 membranes contg. immobilized 30 ± 3 wt.% TiO2, by following anal. both disappearance of absorbable chloro-orgs. (AOX), and mineralization of total org. carbon (TOC) content. Expts. were carried out in PHOTOPERM CPP/313 a pilot plant, using monochromatic irradn. (254 nm) in the absorption range of semiconductor, with an absorbed power of 22 ± 1 W. The initial rate of photodegrdn., both regarding AOX and TOC anal., was studied as a function of the initial concn. of substrate using the linearized form of the Langmuir-Hinshelwood equation, from which the rate consts. k and apparent adsorption consts. K were evaluated. These parameters, which are unable to fit the whole photomineralization kinetic curves, because they account only for initial rates, were employed, as starting values, to optimize, by numerical integration, a kinetic model which considers appearance and disappearance of all intermediates, as if they were represented by a hypothetical single mol., mediating all of them. In this way, two couples of parameters, k1 and K1, k2 and K2 were obtained, relative to the two successive steps of the model (substrate disappearance and mineralization), able to reproduce the whole kinetics satisfactorily. Mean quantum yields of org. carbon mineralization, calcd. by k2 parameters, reach 75, 71, and 31% for the chlorinated phenols in the order reported above, with respect to their max. allowable quantum yields. These values are from 3 to 5 times greater than those measured in lab.-scale expts. thus showing the excellent performance of the pilot-plant employed.